1. Field of the Invention
The present invention relates to an image forming apparatus, and more specifically, it relates to a structure for opening and closing a door that is opened when a paper jam occurs.
2. Description of the Related Art
Some of the conventional image-forming apparatuses such as photocopiers, printers, facsimiles, and multifunctional devices have an apparatus body in which an image forming unit is disposed and a door provided in the apparatus body that can be opened and closed. When maintenance is performed and when a paper jam occurs, the door is opened to open up the inside of the apparatus so as to facilitate maintenance and clearing the paper jam.
For example, an image forming apparatus discussed in Japanese Patent Laid-Open No. 2004-29211 (corresponding to U.S. application No. 2003-235430) has a door that opens downward. The door includes a part of a sheet conveyance unit that conveys a sheet to an image forming unit. When a paper jam occurs, the door is opened and thereby the sheet conveyance unit is opened widely so as to facilitate clearing the paper jam.
FIGS. 10A and 10B are side views of such a conventional image forming apparatus and illustrate a mechanism for opening and closing a door. In FIG. 10A, the door 102 is closed. In FIG. 10B, the door 102 is open.
As shown in FIGS. 10A and 10B, an image forming unit 103 is disposed in an image forming apparatus body (hereinafter referred to as “apparatus body”) 100, and the door 102 is provided in the apparatus body 100 so as to be openable and closable. The door 102 is rotatable around a pivot pin 120 at the lower end. A sheet feeding cassette (not shown) is disposed at the bottom of the apparatus body 100. A sheet conveyance unit (not shown) extends vertically and conveys a sheet from the sheet feeding cassette to the image forming unit 103. The door 102 includes a part of the sheet conveyance unit.
As shown in FIG. 10B, a depression 102b is formed in each side surface 102a of the door 102. A movable hook 109 is provided on each side surface 102a. A movable hook 109 is rotatable around a hook shaft 110. When the door 102 is closed, first, the depression 102b comes into contact with a fixing pin 121 provided in the apparatus body 100. Next, as the door 102 closes, the fixing pin 121 moves along the depression 102b and lifts the movable hook 109. Finally, as shown in FIG. 10A, a depression 109a of the movable hook 109 engages with the fixing pin 121. In this way, the door 102 is locked.
The fixing pin 121 is disposed in each side of the apparatus body 100. The position of the door 102 in relation to the apparatus body 100 in the horizontal direction and the vertical direction is determined by the pivot pin 120.
In the above-described conventional image forming apparatus, the fixing pin 121 of the apparatus body 100 comes into contact with the depression 102b formed in the side surface 102a of the door 102, and then the movable hook 109 engages with the fixing pin 121. Therefore, in consideration of the variation in the position of the fixing pin 121 and in the position of the depression 102b, the inside diameter of the depression 102b needs to be larger than the diameter of the fixing pin 121.
However, in the case where the inside diameter of the depression 102b is larger than the diameter of the fixing pin 121, when the movable hook 109 engages with the fixing pin 121, a gap is left between the depression 102b and the fixing pin 121. Therefore, the door 102 cannot be positioned accurately in the vertical direction and the horizontal direction. Although the positioning in the horizontal direction is performed also by the movable hook 109, the positioning in the horizontal direction cannot be performed accurately because there is a variation also in the position of the movable hook 109.
Therefore, the positioning of the door 102 including the sheet conveyance unit in relation to the apparatus body 100 in the horizontal direction and the vertical direction is performed by the pivot pin 120.
Recently, the number of parts attached to the door 102 has increased. For example, a conveyance unit for two-sided printing is provided in the door 102. If the door 102 is composed of a small number of parts, the door 102 can be distorted due to its inadequate rigidity. It is difficult to position and align the door 102 accurately in relation to the apparatus body 100. When the rigidity of the door 102 is improved in order to prevent the distortion of the door 102, the weight of the door itself increases, and the whole door can be distorted by its own weight.
When the door 102 is distorted and the pivot pin 120 positions the door 102, the accuracy in positioning the door 102 in relation to the image forming unit 103 is lower than the accuracy in positioning the door 102 in relation to a part near the pivot pin 120 because the pivot pin 120 is away from the image forming unit 103.
When the accuracy in positioning the door 102 is low, the sheet conveyance unit in the door 102 cannot be positioned accurately in relation to the image forming unit 103 (for example, a transferring device). As a result, the sheet can skew in the sheet conveyance unit in the apparatus body 100. In such a case, a defect in the image (e.g., scattering of the image) and deterioration in image quality occur.